Why Is Meiosis Important in Biology?
It is a kind of cell division in which sexually reproducing organisms produce gametes like sperm and egg cells. It further undergoes two divisions which result in the formation of four daughter cells. In this kind of division, the number of chromosomes is reduced to half and produces four gamete cells.
This cell division occurs in diploid parents cells which shows it has two daughter cells. In the case of diploid parents, they undergo one DNA replication and two types of meiosis cell division i.e. meiosis 1 and meiosis 2. These two meiotic divisions lead to the formation of four haploid daughter cells which means they consist of half chromosomes of the diploid parent cell.
Type of Meiosis Division
Meiosis cell division takes place in two stages, they are:
Meiosis I:
It is further divided into different Kinds, they are
A. Prophase I:
In this step there occurs disintegration of the nuclear envelope and chromosome condensation starts. They also occur in the appearance of spindle fibre.
B. Prometaphase II:
In this phase there occurs alignment of homologous chromosomes at the equatorial plate which ensure genetic diversity among offspring.
C. Metaphase I:
In this phase homologous chromosomes align at the equatorial plate ensuring genetic diversity among offspring.
D. Anaphase I:
The homologous chromosomes are pulled towards the opposite poles.
E. Telophase I:
In this phase there occurs the disappearance of spindle fibre and by the nuclear envelope reform.
F. Cytokinesis I:
In this phase, two non-identical diploid cells are formed by the segregation of cytoplasm.
Meiosis II:
This is meiosis is further divided into different Stages:
A. Prophase II:
In this phase, chromatin condenses into chromosomes and disintegration of the nuclear envelope occurs. In this phase migration of centromeres occurs to either pole which leads to the reformation of spindle fibre.
B. Metaphase II:
In this phase, chromosomes align themself along the equatorial plate.
C. Anaphase II:
In this phase sister chromatids are pulled towards the opposite pole.
D. Telophase II:
In this phase nuclear envelope undergoes redevelopment and spindle fibre disappears.
E. Cytokinesis II:
At last in this cytokinesis phase cytoplasm and the cell divides and produces four non-identical haploid daughter cells.
At the end of cell division, we are left with four non-identical haploid daughter cells.
FAQs on What Is Meiosis? Definition, Stages & Significance
1. What is meiosis, and why is it essential for sexual reproduction?
Meiosis is a specialised type of cell division that reduces the number of chromosomes in a parent cell by half to produce four genetically unique daughter cells. It is essential for sexual reproduction because it creates haploid gametes (sperm and egg cells). When these gametes fuse during fertilisation, the original diploid chromosome number is restored in the offspring, maintaining the species' chromosome count across generations.
2. What are the two main divisions of meiosis, and what happens in each?
Meiosis consists of two successive nuclear divisions, Meiosis I and Meiosis II.
- Meiosis I: This is the reductional division where homologous chromosomes are separated. It halves the chromosome number from diploid (2n) to haploid (n).
- Meiosis II: This is the equational division where sister chromatids are separated. It is similar to mitosis, and the four haploid cells are formed at the end of this stage.
3. How does Meiosis I differ from Meiosis II?
The primary difference lies in what separates during anaphase. In Meiosis I, homologous chromosomes separate, which reduces the chromosome number by half. In Meiosis II, sister chromatids separate, which is similar to mitosis and does not change the chromosome number of the cells entering this phase. Consequently, Meiosis I starts with one diploid cell and ends with two haploid cells, while Meiosis II starts with two haploid cells and ends with four haploid cells.
4. What is the key difference between mitosis and meiosis?
The key differences between mitosis and meiosis are:
- Purpose: Mitosis is for growth, repair, and asexual reproduction, producing two identical diploid cells. Meiosis is exclusively for producing gametes for sexual reproduction, resulting in four genetically different haploid cells.
- Number of Divisions: Mitosis involves one round of cell division, whereas meiosis involves two rounds (Meiosis I and Meiosis II).
- Genetic Variation: Mitosis produces genetically identical daughter cells. Meiosis introduces genetic variation through processes like crossing over and independent assortment.
5. What is the primary significance of meiosis for a species?
The primary significance of meiosis is twofold:
- Maintenance of Chromosome Number: It ensures that the specific chromosome number of a species is maintained across generations by producing haploid gametes.
- Introduction of Genetic Variation: It creates new combinations of genes through crossing over and the random segregation of chromosomes. This genetic diversity is crucial for the adaptation and evolution of a species.
6. Why is Meiosis I known as the reductional division, while Meiosis II is called the equational division?
Meiosis I is called the reductional division because it reduces the chromosome number from diploid (2n) to haploid (n). This happens when the pairs of homologous chromosomes are separated. Meiosis II is called the equational division because, like mitosis, it separates sister chromatids. The number of chromosomes in the cells at the beginning and end of Meiosis II remains equal (haploid), so there is no reduction in chromosome number during this stage.
7. How does crossing over in Prophase I contribute to genetic diversity?
During Prophase I, homologous chromosomes pair up. Crossing over is the process where segments of DNA are exchanged between these paired non-sister chromatids. This exchange shuffles the genetic material, creating new combinations of alleles on the chromosomes. As a result, the gametes produced are not identical to each other or to the parent cell, which is a major source of genetic diversity in a population.
8. What would be the consequence if gametes were formed by mitosis instead of meiosis?
If gametes were formed by mitosis, they would be diploid (2n), just like the parent somatic cells. During fertilisation, the fusion of two diploid gametes would result in a zygote with double the normal chromosome number (4n), a condition known as polyploidy. This would disrupt the genetic stability of the species, and in most animals, including humans, such a condition is not viable and would prevent the development of a healthy offspring.
